The invention relates generally to interactions between epithelium and mesenchyme, e.g., interactions at hair follicles, and to the processes of hair development and hair cycling.
Epithelial-mesenchymal interactions during development are essential for the induction of organogenesis for many tissues (e.g., kidney, gut, respiratory organ, cutaneous appendage). Among these, the hair follicle provides an excellent model for studying epithelial-mesenchymal interactions because: 1) it is located on the outermost layer of the body, allowing easy access and observation; 2) it has distinct epithelial and mesenchymal components; and 3) a definitive functional assay for in vivo hair induction already exists. (Weinberg, W. C., Goodman, L. V., George, C., Morgan, D. L., Ledbetter, S., Yuspa, S. H. & Lichti, U. (1993) J. Invest. Dermatol. 100, 229–236).
The dermal papilla (DP) is located at the bottom of the hair follicle and is the major mesenchymal component. The DP originates from condensed mesenchymal cells that lie beneath the epithelial hair germ cells (placode) in embryonic skin. These specialized mesenchymal cells are believed to be the source of the dermal-derived signaling molecule(s) involved in hair development and embryogenesis and later in postnatal hair cycling. (Hardy, M. H. (1992) Trends Genet. 8, 55–61).
Hair development during embryogenesis requires a series of reciprocal interactions between the epithelium and the underlying mesenchymal cells. Initially, the dermal mesenchyme signals the epithelium to form the epidermal placode. In response, the epithelium sends a message to the underlying mesenchyme to initiate mesenchymal condensation. The condensed mesenchyme then sends a message back to the epithelium promoting hair elongation. (Messenger, A. G. (1993) J. Invest. Dermatol. 101, 4S–9S).
There is a need in the art to investigate target gene(s) or mesenchymal-derived signaling molecules that have an active role in the dermal condensation and hair growth induction.